The advantages of using a network comprising switching elements that route packets of data through the network on the basis of an address contained within the packets are known. Such networks are commonly called binary routing networks. A specific example is the butterfly or banyan network. In such a network, there exists only one unique path between any two network terminations. The network comprises a plurality of stages each having a number of switch nodes. The stages are interconnected by means of links. Each switch node, upon receipt of a packet, is responsive to the contents of its address field to properly route the packet to the next stage via an interconnecting link.
One system of that type is disclosed in J. S. Turner, U.S. Pat. No. 4,491,945, of Jan. 1, 1985, entitled "Fast Packet Switch". The Turner system is designed to provide integrated voice and data packet communication among a plurality of packet switching networks interconnected by means of digital trunks with each such trunk being terminated by a trunk controller which interconnects to a packet switching network. The patent describes call setup and reply packets used by customers to set up a logical path through the different packet switching networks. The system works using two different types of packets for the communication of data. Trunk packets are utilized for the transmission of information on high-speed digital trunks, and the transfer of information between trunk controllers through a packet switching network is via switch packets which comprise the trunk packet plus additional information used for routing the packet through the packet switching network. A trunk controller is responsive to a trunk packet to form the switch packet and, in particular, to insert into a destination trunk controller field of the switch packet the address used to route the packet through the packet switching network. As the switch packet is routed through the packet switching network, each node, upon receiving the switch packet, examines the destination trunk controller field and communicates the packet to the destinated switch node in a next subsequent stage. Each switch packet communicated from an originating trunk controller is only transmitted to one destination trunk controller.
Whereas the process of allowing each switch packet to be transmitted to only one destination trunk controller gives adequate performance in many situations, there are situations where it is desirable that a packet transmitted from one trunk controller be received by a plurality of destination trunk controllers. For example, in the Turner system, the central processor performing administrative control of the switching network communicates with the various trunk controllers attached to that network via its own trunk controller. Situations arise where it is desirable for the central processor to be able to transmit the same packet to a group of destination trunk controllers or two individual trunk controllers. One such situation is when a conference call function is being performed by the network. In addition, during certain types of maintenance functions, it is desirable to be able to transmit the same packet to all trunk controllers attached to the switching network. In the Turner system, the central processor transmits such packets one at a time to each of the destination trunk controllers. Obviously, such techniques involve large amounts of real time to do so.
Self-routing networks are often used for the interconnection of a plurality of computers, but such networks suffer from the disadvantage that they are unable to transmit a given packet simultaneously rather than in sequence to a number of computers attached to the network. For example, one such simultaneous transmission case is where one computer is transferring a data base to a number of other computers.